How to add Brushes in 2.8
Click Append in File menu
Browse file \ Brush and select brushes you need (b for box select)
In Sculpt mode click on brush preview image and select one




Updated:

Brushes will be saved in you curent file. 


  Thought I had it once but they disappeared once I click on one.


That mean you have not saved your brushes in Startup file. If you need these brushes in each your project - you need to save they in Startup.



Be careful - with brushes all other data (objects, UI and so on..) will be saved as Startup! Preferably create New file, import brushes and then save Startup file.

Blend file with brushes